How to pass items to loop using Jinja2/Flask?

Question

I want to pass a list of pages and loop it in Jinja2 to show all pages of my website. I use Flask to construct and run the app. I followed the official flask documentation, together with this tutorial. However when I try to pass the list and try to loop over it, it does not appear in the rendered html.

What am I doing wrong? How to properly pass the list and loop over it using base.html as a template?

Here is my code with a dummy page list hardcoded:

app.py:

from flask import Flask, render_template

app = Flask(__name__)


@app.route('/')
def index():
    page_list = ['Eins', 'Zwei']
    return render_template('base.html', pages=page_list)


if __name__ == "__main__":
    app.run(port=8000)

And base.html, located in /templates/:

<html>
<head>
<title>Test</title>
</head>

<body>
<h1>All the nice pages</h1>
{% for page in pages %}
<p>{{ page }}</p>
{% endfor %}
</body>
</html>

When I run the app and browse to http://127.0.0.1:8000/, this is what I get:

<html>
<head>
<title>Test</title>
</head>

<h1>All the nice pages</h1>
<body>

</body>
</html>

Something isn't right. Your code works as you'd expect it to. Did you change app.py after starting the application? You'll need to reload it. I'd suggest adding debug=True to your call to app.run(). — dirn
– dirn, Commented Jan 16, 2014 at 16:38
I tried your app and it works just fine, it prints both the page lists to the browser. Reload the app or stop the simultaneous app running in background. — ajknzhol
– ajknzhol, Commented Jan 16, 2014 at 16:41
Also, unrelated, but watch the placement of your HTML tags. Your h1 appears outside the body tag. — dirn
– dirn, Commented Jan 16, 2014 at 16:41

mcbetz · Accepted Answer · 2014-01-16 20:13:41Z

2

This code is totally valid. The important thing is to restart the server if you do changes to lists or dictionaries.

Apart from that, in Flask you can pass any type that is built into Python, be it a list, a dictionary or a tuple.

Here are short example for each of the types that pass more or less the same content:

from flask import Flask, render_template

adictionary = {'spam': 1, 'eggs': 2}
alist = ['Eins', 'Zwei', 'Drei']
atuple = ('spam', 'eggs')

app = Flask(__name__)


@app.route('/')
def index():
    return render_template('base.html', pages=alist)


@app.route('/tuple/')
def tuple():
    return render_template('base.html', pages=atuple)


@app.route('/dict/')
def adict():
    return render_template('base.html', pages=adictionary)

if __name__ == "__main__":
    app.run(port=8000)

answered Jan 16, 2014 at 20:13

mcbetz

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Comments

heisenb0rg · Accepted Answer · 2016-05-05 03:29:48Z

0

I was having this same issue. I use Sublime Text 3 and realized that I didn't automatically convert tabs to spaces. Once I made that change in the user settings, and reran the script, it output the list correctly.

answered May 5, 2016 at 3:29

heisenb0rg

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